O.K. Guys, I just finished rejetting my WR450, wow what a difference! I changed the pilot jet from a 45 to a 48, changed the main jet from a 150 to a 155 (that came with the bike,)and I raised the needle one clip. I'am at 4500ft. and now it starts cold, full choke no throttle, instantly. No hesitation or backfiring and the low end power is even better. I ran it up and down the street to warm it up, then started it several times, its starts instantly with no throttle. I cruised along at a slow steady speed and it was smooth as silk. it is now the most perfect off road bike ever built!